The present invention relates to a ball nose end cutting tool having cutting bit inserts which may be quickly and accurately positioned on a tool holder and secured thereto with ease. Further, the present construction permits the cutting bits to be mounted in a substantially end-to-end relationship for cutting to the center of the tool thereby reducing cutting forces at the center.
Ball nose end mills are used in many metal working applications including mold making where the inherent strength and milling advantages of a fully radiused cutting edge for the copy milling of a mold cavity is best demonstrated. Its ball shape allows the end mill to attack the mold cavity from any angle or direction. The cutting edge when generated through the end of the ball mill becomes helical with rotation. This promotes shearing of the metal to be cut in an efficient manner.
It has heretofore been the practice, in the case of ball nose end milling tools, to secure the cutting bits on a tool holder by brazing. Typically, cutting bits are spaced apart at the center of the ball nose end to permit movement of a grinding tool or fixture when the bits are to be re-sharpened. Because of the brittleness of the high-speed cutting material used for the bits, the bits are susceptible to breakage under cutting pressure because of the gap therebetween. When the cutting bit breaks, there is, aside from the loss of the broken bit, the expense of the time of shutting down the tool to replace the bit.
Further, the concept of indexable inserts presents a problem if the concept were applied to a ball nose end mill because of the need for clamps over the inserts for heavy roughing which would restrict chip flow. Staggering several indexable inserts around the ball nose radius and overlapping portions of the previous insert in order to encompass the entire radius would inhibit chip flow, would still only permit no more than one insert to extend to the center line of the ball nose, and would reduce the accuracy of the milling process.
Thus, it is an object of the present invention to provide a ball nose end cutting tool using removable cutting bits which are less susceptible to breakage in usage. Another object of the invention is to provide a construction whereby cutting bits may be accurately installed and replaced with ease. Further, it is an object of the present invention to employ opposed cutting bits which cut from the outside periphery of the tool holder inwardly to the center thereby reducing the cutting forces at the center and providing for improved plunging capability.